Design for a shelf unit



FIG. 1 is a front elevational view of a shelf unit showing my new design;

FIG. 2 is a right side elevational view, the left side being a mirror image thereof;

FIG. 3 is a perspective view, the opposite side being a mirror image thereof; and

FIG. 4 is an enlarged fragmentary front elevational view of the left corner. 

The ornamental design for a shelf unit, as shown and described. 